The invention is in the field of integrated circuit structures and specifically in the field of dielectrically isolated integrated circuit structures.
Integrated circuit structures may be described as comprising a number of laterally spaced islands electrically isolated from each other so that an independent active or passive device can be formed at each island. One way of electrically isolating the islands from each other is to use PN junctions both underneath the islands and between the islands. Integrated circuits of this type are called PN junction isolated IC's. Another way of electrically isolating the islands from each other, which has significant advantages over the PN junction isolation, is to separate the islands from each other laterally by grooves of an electrically isolating matter. The islands are then electrically isolated from each other by the combination of these grooves and a PN junction region which is underneath the islands and is intersected by the grooves. This invention is directed to such dielectrically isolated integrated circuit structures and specifically relates to such structures using grooves of an electrically isolating matter that have a particularly advantageous shape, size, makeup and location relative to the PN junction region.
In one particular embodiment, the invention relates to a semiconductor material structure comprising a semiconductor material substrate of one conductivity type (e.g., P-type) and a semiconductor material layer of opposite conductivity type (e.g., N-type) disposed over a top, major surface of the substrate. An isolating PN junction region (which can also be called a depletion region, or a space-charge region) having a finite thickness extends laterally along the structure and forms an isolation barrier between regions of the substrate and layer. Closed annular grooves of an electrically isolating matter extend downwardly into the structure from the top surface of the layer, intersect the PN junction region, and divide a top portion of the structure into a number of islands which are laterally spaced from each other by the width of the grooves. Moreover, the islands are electrically isolated from each other by said grooves and said PN junction region. The grooves have shaped or curved bottoms, i.e., the distance by which each groove extends downwardly into the structure varies along at least a major portion of the width of the groove, and may vary over the entire width of the groove. Each groove has a bottom which is within one micron of the PN junction region. The interface between the groove and the semiconductor materal is a surface which intersects the PN junction region non-normally. The same interface surface intersects the top surface of the islands also at a non-normal angle. This same surface is slanted or curved in vertical section at the PN junction region so as to linearly or differentially expand the PN junction region intersected by that surface. The underside of the grooves may be rounded such that the groove bottom has substantially zero width. The grooves can be formed such that the interface surface discussed above has two slopes within one micron of the PN junction region in a vertical plane. That same interface surface has a radius of curvature in the vertical plane which is in the range of one centimeter down to one micron. In vertical section, the groove may be V-shaped. The electrically isolating matter of the groove may be ambient air or vacuum, or it may be an oxide (or nitride) formed from the adjacent semiconductor material of the structure. When that electrically isolating matter is such oxide (or nitride), the top surface of the oxide (or nitride) is preferably coplanar, or substantially coplanar, with the top surface of the islands to facilitate providing electrical contact to the islands. Such oxide (or nitride) grooves may be in-situ formed by ion implantation or precision thermal diffusion or oxidation (or nitridation) at elevated temperatures, e.g., at about 700.degree. C. or higher in an oxygen (or nitrogen) containing atmosphere.